1. Field of the Invention
The present invention relates to a high strength poly-m-phenylene isophthalamide fiber and a process for producing the same. More particularly, the present invention relates to a new type of poly-m-phenylene isophthalamide fiber having a much higher tensile strength than that of conventional poly-m-phenylene isophthalamide fibers, and a new process for producing the same.
2. Description of the Related Art
It is well known from, for example, U.S. Pat. Nos. 3,287,324, 3,300,450, 3,560,137 and 4,073,837, that conventional poly-m-phenylene isophthalamide fibers, which are available under a registered trademark of TEIJINCONEX or NOMEX, exhibit an excellent heat-resistance and a superior flame-resistance, and are utilized in various fields, for example, clothing and industrial materials.
It is also known, however, that the conventional poly-m-phenylene isophthalamide fibers have a relatively low mechanical strength, for example, a tensile strength of about 5.5 g/denier or less, and therefore, utilization of the fibers is restricted in specific fields in which the fibers are required to exhibit a very high mechanical strength, for example, reinforcing fibrous materials for rubber products and synthetic resinous products, and substrate cloth for bag filter felts.
To eliminate the disadvantages of the conventional poly-m-phenylene isophthalamide fibers, poly-p-phenylene terephthalamide fibers are provided. The poly-p-phenylene terephthalamide fibers exhibit a very high mechanical strength, for example a tensile strength of about 20 g/denier or more. These poly-p-phenylene terephthalate fibers, however, can be produced only at a very high cost, and exhibit a very small ultimate elongation of about 5% or less. Accordingly, the poly-p-phenylene terephthalamide fibers are not usable in fields in which the fibers are required to have an ultimate elongation of more than about 5%. Also, the poly-p-phenylene terephthalamide fibers are disadvantageous in that fibrillation thereof is easily caused.